Steerable Downhole Hammer Bit

ABSTRACT

A drill bit for use with a pneumatic hammer used in horizontal directional drilling operations. A compact forward face is formed on the first end of the drill bit. The forward face reciprocates against a face of a borehole. A steering face is disposed behind the forward face and is concave adjacent its first end and convex adjacent its second end, with a smooth transition between the two regions. The body has a circular profile at its second end. The drill bit displaces cobble and small rocks encountered, rather than breaking them, enhancing steering in mixed conditions.

SUMMARY

The present invention is directed to a method comprising providing a drill bit comprising a body having opposed first and second ends and opposed steering and external faces formed between the first and second ends. The steering face has a concave portion that transitions into a convex portion. The concave portion starts at the first end and the convex portion terminates at the second end. The method further comprises attaching the drill bit to an end of a downhole tool comprising a fluid driven hammer, lowering the drill bit underground, thrusting the drill bit forward in a first direction while rotating the drill bit, thrusting the drill bit forward in a second direction without rotation, and thrusting the drill bit forward in the second direction while rotating the drill bit.

The present invention is directed to a system comprising a drill bit and a fluid driven hammer connected to the drill bit. The drill bit comprises a body having opposed first and second ends and opposed steering and external faces formed between the first and second ends. The steering face has a concave portion that transitions into a convex portion. The concave portion starts at the first end and the convex portion terminates at the second end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a horizontal directional drilling operation.

FIG. 2 is a front perspective view of a drill bit of the present invention.

FIG. 3 is a front elevation view of the drill bit of FIG. 2.

FIG. 4 is a cross-sectional view of the drill bit of FIG. 3 taken along line A-A.

FIG. 5 is a side elevation view of a body of the drill bit of FIG. 2.

FIG. 6 is a cross-sectional view of FIG. 5, taken along line B-B.

FIG. 7 is a cross-sectional view of FIG. 5, taken along line C-C.

FIG. 8 is a cross-sectional view of FIG. 5, taken along line D-D.

FIG. 9 is a top plan view of the drill bit of FIG. 2.

FIG. 10 is a top plan view of the drill bit of FIG. 2. The drill bit is attached to a downhole tool.

DETAILED DESCRIPTION

With reference to FIGS. 1-2, a drill bit 10 for use in horizontal directional drilling operations is shown. The drill bit 10 is attached to a front end 12 of a downhole tool assembly 14. The downhole tool assembly 14 includes a chuck 86, a fluid driven hammer 16, a transmitter housing 17, and a bent sub 94 (FIG. 10). The hammer 16 operates by repeatedly striking a face 18 of an underground borehole 20 with the drill bit 10 to form the borehole 20.

The drilling operations are powered by a directional drilling machine 22 at a ground surface 24. The drilling machine 22 connects pipe sections together at the ground surface 24 to form a drill string 26. A first end 28 of the drill string 26 is connected to the drilling machine 22 and a second end 30 of the drill string 26 is connected to the downhole tool 14. In operation, the drilling machine 22 will send air, an air-foam mixture, or fluid through the drill string 26 to the downhole tool 14 to power the hammer 16. As will be further described below, the drill bit 10 is configured to allow the drill bit 10 to steer while drilling in rocky conditions using the hammer 16.

Continuing with FIG. 2, the drill bit 10 comprises a body 32 attached to a shank 34. The drill bit 10 may be made of a wear resistant metal, such as steel. The body 32 has a first end 36 and an opposed second end 38. The shank 34 is joined to the second end 38 of the body 32. The shank 34 and body 32 may be formed as separate pieces, or as a single piece. A steering face 40 and an opposed external face 42 are formed between the first and second ends 36, 38 of the body 32. The external face 42 has a rounded outer surface. A longitudinal axis 44 of the drill bit 10 is also shown via a dashed line in FIG. 2. The second end 38 of the body 32 is symmetric about the longitudinal axis 44 of the drill bit 10 and the first end 36 is asymmetric with respect to the longitudinal axis.

With reference to FIGS. 2-4, a forward face 46 is formed on the first end 36 of the body 32. The forward face 46 makes first contact with the face 18 of the borehole 20 (FIG. 1) during drilling operations. The forward face 46 is bounded by a narrow leading edge 48 and a wider trailing edge 50. The forward face 46 is also oriented at an angle between 0-15 degrees to a plane that is orthogonal to an axis of rotation of the drill bit 10. The drilling machine 22 rotates the drill string in a clockwise direction, which in turn rotates the drill bit 10 in a clockwise direction about its longitudinal axis 44. This allows the leading edge 48 to contact the face 18 of the borehole 20 before the trailing edge 50 during operation. Allowing the leading edge 48 to make first contact with the face 18 of the borehole 20 prevents churning that can impede forward progress by the drill bit 10. Allowing the leading edge 48 to make first contact with the face 18 of the borehole 20 also helps to prevent disturbances of the surrounding underground formation during operation.

The edges 48, 50 extend at a non-zero angle between the first end 36 and the second end 38. Due to this, the area of the external face 42 increases from the first end 36 to the second end 38. This is because the distance between the leading edge 48 and the trailing edge 50 increases as the edges move from the first end 36 to the second end 38. The feature allows the edges 48, 50 of the drill bit 10 to bite into the surrounding rock formation during operation.

A brow 52 is formed on the external face 42 of the body 32 proximate the forward face 46 (FIG. 2). The drill bit 10 is wider at its brow 52 than at other regions of its external face 42 (FIG. 5). The wider brow 52 provides a larger surface area for the forward face 46 and deflects debris or rocks within the borehole 20 away from the remainder of the external face 42. A plurality of carbide inserts 54 are also attached to the forward face 46. The carbide inserts 54 help enhance cutting during boring and help reduce wear on the drill bit 10. Carbide inserts 54 may also be attached to the leading edge 48, as shown in FIG. 3. The longitudinal axis 44 and the steering face 40 are also shown in FIG. 3.

Turning now to FIGS. 4-8, the steering face 40 of the body 32 is shown in more detail. The drill bit 10 transitions smoothly from a forward face 46 to a second end 38 having a circular profile. The steering face 40 does not have a hollowed out center. Rather, the steering face 40 has a concave portion 58 that extends from the first end 36 and transitions into a convex portion 60. The convex portion 60 terminates at the second end 38. The steering face 40 has a circular profile at its second end 38, as shown in FIG. 8. This shaping of the steering face 40 allows a relatively compact forward face 46 to be formed at the first end 36. A rear view of the forward face 46 is shown in FIG. 6.

The concave portion 58 transitions into the convex portion 60 at a transition zone or inflection 62. The transition zone 62 is formed on or proximate the longitudinal axis 44 of the drill bit 10, as shown in FIGS. 5 and 7. The transition 62 is also positioned closer to the first end 36 than the second end 38. In alternative embodiments, the transition zone 62 may extend above or below the longitudinal axis 44, rather than in alignment with that axis. Or the transition zone 62 may coincide with the center of the steering face 40. Or the transition zone 62 may be situated closer to the second end 38 than the first end 36.

Viewed from ahead of the bit along its longitudinal axis, the concave portion 58 presents a footprint that is fully contained within the footprint of the convex portion 60. Thus, as the drill bit 10 is thrust forward during drilling operations, the cross-sectional area of the borehole 20 surrounding the drill bit 10 gradually increases.

The relatively small area of the forward face 46 aids in drilling into rocky or mixed soil conditions, such as cobblestone. Cobblestones are hard rocks typically surrounded by compacted sand. The forward face 46 makes up less than 35% of the drill bit's 10 maximum cross-sectional area. The sizing allows the forward face 46 to break into fines or sand between cobblestones, rather than chipping or cutting the stones themselves. High frequency percussion against the fines allows the bit 10 to move the stones radially out of the bore path. Orderly rearrangement of the mixed rock formation, rather than cutting through the rock helps prevent the borehole from collapsing during operation and requires less torque and energy. Movement is possible because the percussion rearranges the cobbles into a tighter formation, by allowing the sand between the cobbles to drop into the borehole 20 and be removed from the bore by the exhaust stream from the drill bit 10. The drill bit 10 may also be used in loamy or sandy conditions.

Once the forward face 46 breaks between the stones, the concave portion 58 of the drill bit 10 pushes or reorients the position of the cobbles in order to make way for the rest of the drill bit 10. Because the distance of the edges 38, 40 increases between the first end 36 and the second end 38, the area of the drill bit 10 that bites into the surrounding formation increases towards the second end 38. By the second end 38, at least 40% of the drill bit 10 is breaking into the surrounding rock formation. The drill bit 10 creates a circular borehole 20 (FIG. 1) because the second end 38 of the drill bit 10 has a circular profile.

Turning back to FIG. 2, the steering face 40 and external face 42 are slanted or angled at a non-zero angle relative the longitudinal axis 44 of the drill bit 10. Having a slanted steering face 40 allows the drill bit 10 to steer during operation. While drilling, the drill bit 10 is rotated at a steady rate while it reciprocates against the face 18 of the borehole 20 (FIG. 1). The drill bit 10 produces a straight bore path while it is rotated. In order to change the direction the bore path, the steering face 40 is rotated to face the direction an operator desires to drill. The drill bit 10 is then reciprocated against the face 18 of the borehole 20 without being rotated. The slant of the steering face 40 will direct the drill bit 10 towards the desired direction. Once the drill bit 10 is positioned in the desired direction, the drill bit 10 may be rotated again in order to return to a straight bore path.

Unlike traditional hammer drill bits, the drill bit 10 does not require any rocking or carving motion to achieve steering. Portions of the borehole 20 are more likely to collapse when carving against the rock to achieve steering. The collapsed borehole 20 may cause the drill bit 10 to tend to rise upward during operation even as they are steered in a downward direction.

With reference to FIGS. 4 and 8-9, the drill bit 10 has an internal flow passage 64 formed along its longitudinal axis 44. The flow passage 64 is connected to a plurality of passages 66 formed in the body 32 of the drill bit 10. The passages 66 open into exhaust ports 68, 70 formed on the external face 42 of the drill bit 10 (FIG. 9). The passage 66 shown in FIG. 4 extends at a non-zero angle relative to the flow passage 64.

Continuing with FIG. 9, the ports 68 vent exhaust from the hammer 16 towards the forward face 46. The air may escape by passing around the forward face 46 of the drill bit 10 and back towards the opening of the borehole 20 at the ground surface 24. The rear facing exhaust port 70 vents air directly towards the opening of the borehole 20 at the ground surface 24. In other embodiments, not shown in the Figures, one or more or all of the ports formed in the external face may discharge toward the first end. Alternatively, one or more or all of these ports may discharge towards the second end. The drill bit 10 may not reciprocate properly if the air cannot vent from the bit. The drill bit 10 is provided with multiple ports 68, 70 so that venting of air is not interrupted should a single port become clogged.

The exhaust ports 68 are formed within channels 72 formed in the external face 42. The channels 72 are open-ended, and extend between the first end 36 and the second end 38 of the body 32. The rear facing exhaust port 70 is positioned within a channel 74. The channel 74 only opens on the second end 38 of the body 32. The channels 72, 74 help direct air venting from the drill bit 10 into the borehole 20.

A through-hole 76 may also be formed in the body 32 of the drill bit 10. The through-hole 76 is an open-ended rectilinear passage that interconnects the steering face 40 and the external face 42. The through-hole 76 opens on the steering face 40 proximate the transition zone 62. A pull-back adapter (not shown), such as that described in U.S. Pat. No. 9,611,696 issued to Crane et al., and incorporated herein for reference, may be installed within the through-hole 76.

Continuing with FIG. 4, a foot valve 78 may be positioned within the shank 34 of the drill bit 10, and a shuttle valve 80 may be positioned above the foot valve 78. The valves 78, 80 control pneumatic timing of the hammer 16 by regulating the flow of air into the flow passage 64. When the hammer 16 is operating, the shuttle valve 80 moves forward towards the body 32 and allows air to pass through the drill bit 10. When the hammer 16 is not operating, the shuttle valve 80 moves rearward and seals fluid from entering the hammer 16 through the drill bit 10.

With reference to FIG. 9, the shank 34 of the drill bit 10 includes front and rear external splines 82, 84. The splines 82, 84 mate with internal splines (not shown) formed in a chuck 86 (FIG. 10) attached to the front end 12 of the downhole tool 14. The splines 82, 84 prevent the drill bit 10 from rotating relative to the downhole tool 14, while allowing the drill bit 10 to move longitudinally relative to the tool 14. The drill bit 10 moves longitudinally relative the downhole tool 14 so that it may reciprocate against the face 18 of the borehole 20. The maximum cross-sectional dimension of the second end 38 of the drill bit 10 is greater than the maximum cross-sectional dimension of the shank 34. The larger area of the second end 38 prevents the chuck 86 from moving pas the second end 38 of the drill bit 10.

Turning now to FIG. 10, the downhole tool 14 may also include a beacon or transmitter housed within the transmitter housing 17. The beacon is preferably a magnetic dipole transmitter. The beacon transmits a locating signal to an above ground tracker during operation. The signal may contain information such as the location, pitch, roll, and yaw orientation of the drill bit 10 and housing 17. The signal may also provide the temperature and battery life of the beacon to the above-ground tracker. The transmitter housing 17 may have a cover 90 to permit access to the beacon, if needed.

The hammer 16 may be attached to the chuck 86 and the transmitter housing 17 may be attached to a rear end of the hammer 16, as shown in FIG. 10. The housing 17 may comprise an internal passage (not shown) that is in fluid communication with the hammer 16, the drill bit 10, and the drill string 26.

At its brow 52, the drill bit 10 has a greater width than either the downhole tool 14 or the drill string 26. This configuration results in the drill bit 10 cutting a borehole 20 that has a cross-sectional dimension that is greater than the cross-sectional dimension of the downhole tool 14. Clearance between the downhole tool 14 and the walls of the borehole 20 reduces friction during drilling.

With reference to FIGS. 1 and 10, the drill bit 10 may be used with the drill string 26 comprising a single rod or a two-pipe drill string comprising an inner and an outer rod. If the drill bit 10 is used with a two pipe drill string 26, the inner rod rotates the drill bit 10 relative to the housing 17 and the hammer 16.

The sub assembly 94 is attached to the rear end 92 of the transmitter housing 17 in FIG. 10. Alternatively, the sub assembly 94 may be positioned between the transmitter housing 17 and the hammer 16. The sub assembly 94 may be bent at an angle of 1-2 degrees relative the housing 17 and hammer 16. The sub assembly 94 enhances the steering capabilities of the drill bit 10 during drilling operations.

Drilling through rock under mixed conditions without the use of a hammer 16 may require the use of large drilling machines and large quantities of drilling mud. Such machines typically weigh over 7,000 pounds and have a large footprint. Large drilling machines may not fit well in urban or semi-urban areas and it may not be possible to use large quantities of drilling mud in such areas.

In contrast, a hammer 16 can drill through rock or mixed conditions when used with a small drilling machine, which may weigh 7,000 pounds or less. Use of a smaller machine is possible because an underground hammer 16 requires less power than might be required to push a drill string 22 from above ground.

Changes may be made in the construction, operation and arrangement of the various parts, elements, steps and procedures described herein without departing from the spirit and scope of the invention as described in the following claims. 

1. A method comprising: providing a drill bit comprising a body having opposed first and second ends and opposed steering and external faces formed between the first and second end, in which the steering face has a concave portion that transitions into a convex portion, in which the concave portion starts at the first end and the convex portion terminates at the second end; attaching the drill bit to an end of a downhole tool comprising a fluid driven hammer; positioning the drill bit within an underground zone; thrusting the drill bit forward in a first direction while rotating the drill bit; thrusting the drill bit forward in a second direction without rotation; and thrusting the drill bit forward in the second direction while rotating the drill bit.
 2. The method of claim 1 in which the underground zone contains cobblestones.
 3. The method of claim 1 further comprising reciprocating the drill bit against a face of the underground zone using the fluid driven hammer.
 4. The method of claim 1 further comprising venting air from the drill bit into the underground zone.
 5. The method of claim 1 further comprising venting an air-foam mixture from the drill bit into the underground zone.
 6. A system comprising: a fluid driven hammer; and a drill bit disposed in force-transmitted relationship to the hammer, comprising: a body having opposed first and second ends and opposed steering and external faces formed between the first and second end, in which the steering face has a concave portion that transitions into a convex portion, in which the concave portion starts at the first end and the convex portion terminates at the second end.
 7. The system of claim 6 further comprising a drilling machine and a drill string having opposed first and second ends, the first end being operatively connected to the drilling machine and the second end being connected to the hammer.
 8. The system of claim 6 further comprising a magnetic dipole transmitter installed within a housing connected to the hammer.
 9. The system of claim 6 in which a chuck is positioned between the hammer and the drill bit.
 10. The system of claim 6 in which the second end of the body is symmetric about a longitudinal axis of the drill bit and the first end is asymmetric with respect to that axis.
 11. The system of claim 6 in which the steering face is positioned at a non-zero angle relative a longitudinal axis of the drill bit.
 12. The system of claim 6 in which at least one fluid port is formed on the external face.
 13. The system of claim 12 in which a flow passage is formed along a longitudinal axis of the drill bit, in which the flow passage is connected to at least one passage that extends at a non-zero angle to at least one fluid port formed on the external face.
 14. The system of claim 12 in which the at least one fluid port is formed in a channel that extends from the first end to the second end of the body.
 15. The system of claim 6 further comprising a shank joined to the second end of the body.
 16. The system of claim 15 in which the second end of the body has a maximum cross-sectional dimension that exceeds the maximum cross-sectional dimension of the shank.
 17. The system of claim 6 in which a rectilinear passage within the body interconnects the external face and the steering face.
 18. The system of claim 17 in which the rectilinear passage opens on the steering face proximate the zone of transition between the convex portion and the concave portion.
 19. The system of claim 6 in which a forward face is positioned at the first end of the body, in which the forward face is bounded by a leading edge and a trailing edge, wherein the leading edge has a width less than a width of the trailing edge.
 20. The system of claim 19 in which the leading edge and the trailing edge extend at a non-zero angle between the first end and the second end of the drill bit.
 21. The system of claim 6 in which the second end of the body has a circular profile.
 22. The system of claim 6 further comprising an underground terrain containing cobblestones and having a borehole formed therethrough, in which the hammer and drill bit are situated within the borehole.
 23. The system of claim 6 in which the transition from the concave portion to the convex portion is made closer to the first end than the second end. 